An internal combustion engine that powers an automotive vehicle may comprise a liquid cooling system for removing waste heat from the engine. Such a cooling system may comprise a pump operated by the engine, a radiator, and a thermostat valve. As the pump circulates liquid coolant through the system, engine heat is transferred to coolant passing through engine coolant passages. When the engine has reached operating temperature, the thermostat valve opens to allow coolant to flow through the radiator where heat is transferred from the coolant to ambient air passing across exterior surfaces of the radiator. Hence, the thermostat valve functions to restrict coolant flow to the radiator until the engine has heated the coolant to a temperature corresponding to the operating temperature of the engine. This allows a cold engine to reach operating temperature more quickly. Once a thermostat valve has fully opened, the temperature of the coolant, and hence that of the engine, can fluctuate over a range of operating temperatures determined by various factors such as the size of the radiator, the rate at which the pump pumps liquid coolant through the radiator, how the engine is being operated, and ambient air temperature. Should the operating temperature fall below this range, the thermostat valve will once again restrict flow to the radiator in an effort to restore operating temperature.
Certain thermostat valves have bi-metal or wax-pellet actuators. Those valves may possess certain disadvantageous operating characteristics, including relatively slow response times and relatively wide switching hysteresis. Such characteristics endow a valve with a wider band of temperatures over which the valve may operate between closed and open positions. Hence, they may exhibit relatively loose temperature regulation.